From Algorithms to Working Programs on the Use of Program Checking in LEDA

LEDA [MN95, MNU97, MN98] is a collection of implementations of data structures and combinatorial algorithms. In the almost ten years of the project we translated hundreds of algorithms into programs. For the purpose of this paper an algorithm is the description of a problem solving method intended for a human reader and a pwgram is a description intended for machine execution. Clearly, algorithms and programs are quite different animals; algorithms are formulated in natural language and are published in papers and books, and programs are written in computer languages and are executed on machines. We expected the process of implementation to be tedious and time-consuming, indeed, it was, but not intellectually challenging. We now believe that the implementation process is very difficult and challenging. We encountered the following difficulties.